Unstable rock slopes along transportation routes in rocky terrain are hazards requiring carefully selected maintenance techniques if safety against rock falls is to be improved at reasonable cost. The paper reviews the causes of rock falls and methods of dealing with them in North American and European highway and railway practice. Methods are classified as those that: (a) stabilize slopes or prevent rocks from moving out of place, (b) protect the right-of-way by keeping rocks that do move out of place from reaching the roadway, and (c) warn or signal traffic when rocks arrive at the vicinity of the roadway. Methods of stabilization, protection, and warning are described and illustrated. Some of these methods can be combined for increased safety at a single site. Guidelines are suggested to organize an effective program to guard against rock falls. Steps in planning, deciding on the priority of sites to be treated, and choice of treatment methods at particular sites are all discussed. Desirable records and measurements are outlined. The paper is intended to be a practical reference for practising engineers.